The purpose of the invention is a device for continuous movement of objects with symmetry of revolution. One of the target applications is the inspection of cylindrical objects at a high speed.
Putting into movement in this case means a combined translation and rotation movement; objects rotate at the same time as they move forwards, for example to present their entire lateral surface (for example cylindrical) to sensors that will check their appearance or characteristics. It is desirable to have a device enabling a large flow of objects on a production or inspection line, by minimizing manipulations of these objects that can follow each other, very close together, in a continuous flow. Therefore, the required movement type must enable continuity of the production flow and displacement of each object at the same time. The device that satisfies this problem must guarantee uniformity of movement—which must be perfectly continuous both in translation along the main axis of the object, and in rotation about this axis—for example to enable a good quality inspection (good quality images obtained in the visual and inspection application), even at high rate, despite constraints imposed on the advance speed of the objects. The design of this type of device must be based on a simple principle, and its operation must be easy to adjust.
Conveyor belts and other conveyance devices are well known, but the need to rotate the objects at the same time as they are being translated after orienting them correctly causes special problems. The production of a system rotating and translating objects at the same time is not easy since if two different forces are to be applied to the object, the rotation and translation movements oppose each other which causes friction that reduces the smoothness of the final movement. However, there is a solution available in “centerless” grinding machine tools, that applies a rotation movement to cylindrical parts by skew applied friction. In this case, the parts also move longitudinally. But this is only possible if the parts are sufficiently long. Furthermore, there is no guarantee of the flow continuity.
This principle is repeated in some inspection systems like that patented by the Rohrer Inc Company (US) in U.S. Pat. No. 5,249,912 “Inspection apparatus” published on May 10, 1993. The double movement is then applied to the cylindrical object by means of a belt that entrains objects in rotation by friction and a double guide above and through this belt that applies a translation movement to these objects. The application divulged in this patent was an eddy currents inspection. The solution divulged in this patent consists of orienting the cylindrical objects by making them slide under an inverted channel pathway that aligns their axes with the direction of advance, and rotation is achieved by passing the objects on an endless belt that moves in a lateral direction (but not perpendicular) and forces a rolling movement on them.
Unfortunately, this system comprises limitations due to friction between objects and the guide. This friction prevents a perfectly regular helical movement at a high rate. The simultaneous rotation/translation movement imposed by the endless belt on an object that is stopped by a guide, regardless of the type of guide, necessarily generates friction between the object and the guide (inverted channel in the patent mentioned above) that disturbs the uniformity of this movement and cause jerks and vibrations on the object, particularly at high speeds. This friction and its disturbing consequences can then blur the images of the object taken with an optical detector, for example in a visual inspection. In this case, and particularly at high speeds, this device cannot produce the very high quality images necessary for a high performance inspection. Furthermore, if severely damaged parts appear, they may be entrained very irregularly, and the rotation movement would be hindered or even actually stopped. The part is then very badly entrained since apart from the fact that parasite friction affects the movement of the guide, there is only a single line of contact between the part and the belt. Finally, the space available to contain inspection sensors is reduced due to the presence of the guide (for example a simple or double rail) and may be insufficient for inspection applications using sensors other than those described in the Rohrer patent.
The device according to the invention is intended to improve the movement, and particularly to completely solve these disturbing friction problems by eliminating defects inherent to prior devices.